1. Field of the Invention
The present invention relates to a liquid jet recording apparatus and more particularly to a type of liquid jet recording apparatus comprising an ink jet type recording head, a subsidiary tank for feeding ink to the recording head and a main tank containing ink to be supplied to the subsidiary tank.
2. Description of the Prior Art
The recording head used in ink jet recording apparatus has a jet flow channel provided with an ink jet orifice at its tip end for forming flying droplets. During a rest time of operation of the apparatus, the ink in the jet flow channel often gets dried into solid which blocks the flow channel. Thus, a trouble called blocking is caused thereby. Also, the apparatus often suffers a trouble of meniscus retrogradation. As is well known, a meniscus is formed in the fore part of the ink jet channel. Vibration, impact and other force applied to the apparatus during the time the apparatus is being transported often causes the formed meniscus to move backwards which may result in poor printing or inability to effect printing. This is the trouble of meniscus retrogradation. Even when the apparatus is in printing operation, trouble may be caused by fiber dust from the recording paper, dust from the atmosphere and foreign matters in the ink. These dusts and foreign matters sometimes block the ink flow channel, which also brings about poor printing or inability to effect printing.
Such trouble, when once occurred, must be removed by employing any suitable means. One of the methods conventionally used for this purpose is to use a negative pressure applying means such as suction pump or suction bomb. Such negative pressure applying means is attached to the fore end of the ink flow channel every time there is trouble to suck the ink and to carry out cleaning of the blocked channel. Another conventional method is to use a liquid in which the ink is soluble. The ink dissolving liquid is applied to the solidified ink to dissolve it thereby restoring the condition of the channel to its original state for good jet of ink droplets.
However, the conventional methods mentioned above have some drawbacks. These methods are effective to recover good printing conditions only when some amount of ink is present in an ink tank communicating with the recording head. If the ink tank is vacant, an ink sucking operation will cause air to be sucked into the liquid passage within the recording head. In this case, the printing apparatus also produces a poor result or becomes unable to effect printing. The ink tank may be emptied by over-suction. In the case of apparatus having a movable ink tank and a stationary ink tank, if the connection line between the two tanks is blocked, no ink can be supplied to the movable tank from the stationary one. Under such condition, the movable tank will be emptied soon. Also, there is the case wherein the movable ink tank is emptied by ink evaporation in the movable ink tank itself and also in the connection line, or the like. When there remains no ink in the ink tank, an application of ink suction for removing a blockage of printing will cause another important problem. Therefore, in this case, it has conventionally been required to supply ink to the emptied movable tank, as a pretreatment, prior to the suction. However, this involves a problem in particular for such type of apparatus which has a separate ink suction mechanism provided only for recovery of the printing condition and operable independently of an ink feeding mechanism. In this case, when a trouble of poor printing or printing inability occurs in the apparatus, man can not determine which mechanism should be used, ink feeding mechanism or ink suction mechanism unless the cause for the occurred trouble is ascertained. If an ink suction is done erroneously although the movable ink tank contains no ink, then a permanent problem of inability to print may be caused thereby. To prevent such a important problem, there has already been proposed, for example, an apparatus provided with means for detecting the volume of ink remaining in the movable and stationary ink tanks. However, the provision of such additional detection means has made the apparatus very complicated and difficult to be compactly manufactured at a reduced cost.
In the case of ink jet recording apparatus, it is essentially important to smoothly and stably supply ink to the recording head during operation. It is impossible to form flying droplets from the ink jetted from the orifice with high reproducibility and in a stable manner and, therefore, to obtain high quality recorded images unless smooth and stable ink supply to the recording head is assured. With respect to the smooth and stable ink supply, all of the known apparatus are unsatisfactory and still have some problems to be solved.
Further, in the case of such type of apparatus in which the recording head reciprocates at a high speed, it has been found that the reciprocation of the recording head has a great adverse effect on the ink supply to the recording head from the ink tank. For example, the ink supply to the recording head is occasionally interrupted and the amount of ink supplied to the head is made unstable. There is also known in the art a type of apparatus designed as a closed system in which the liquid flow line extending from the ink tank to the tip end of the recording head is completely closed from the atmosphere except for the jet orifice formed at the fore part of the line. For such closed system, it is essential to assure a smooth and prompt ink supply following the ink jetting operation of the recording head during recording. With respect to this point, apparatus hitherto known is not satisfactory and has some problems to be solved.